Masumi Sera (世良 真純 ,Sera Masumi) is a character in the manga and anime franchise Detective Conan. She is a self-proclaimed high school detective and practitioner of the martial art Jeet Kune Do. After making a mostly correct deduction during a murder case, she transfers to Ran's high school class. She seems to know that Conan is a detective.

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Masumi Sera is a high school detective and skilled at Jeet Kune Do, the martial art founded by Bruce Lee. She can fight in the same level as Ran. She transfers to Ran and Sonoko's class at Teitan High. Since three years ago, she'd been living in America with her parents, presumably due to Akai infiltrating the Black Organization. She claims she'd rather live in Japan where she was born and raised, so she came to Tokyo and is currently living in a hotel.

Sera has a cheery, sociable, boyish personality and is well liked by her classmates at Teitan High. On their first meeting, Sera fails to correct Sonoko's mistaken impression that she is a man and even makes it worse by declaring that Ran is "[her] type". Her rather boyish appearance - especially in relation with her flat chest - is a bit of a touchy subject to Sera, who claims that her mother's bust size is rather well developed and keeps expressing her hope that someday her own chest size will similarly change for her.

Sera is quite quick-minded, coming up with clever plans and adapting them to sudden changes rapidly. Sera seems to be prone to dramatics like most detectives are, but perhaps to a lesser degree than Shinichi or Heiji as she bluntly says who the criminal is without preamble. On the other hand, Sera is tough to the point that she is willing to risk all to achieve a successful conclusion of a case. In one instance, she purposefully lured a hostage-taker into a sniper's sight with a smile, hoping he would be shot without showing any apprehension about his possible demise.

Although she has crime scene experience, Sera seems to be less skilled as a detective than Shinichi or Heiji, apparently missing a critical clue that was necessary to understand how the murderer's setup worked, although Conan opines that Sera purposely made an error in order to test him. In some degree, she seems to like rivalry or contests to see who the winner is.

At first, she wears a fedora and a dark jacket which gives her an androgynous appearance. When she transfers to Teitan High, she gets rid of her fedora and wears female clothing. Her hair is dark, wavy, and short; it doesn't even touch her shoulders. Even then, she is rather tomboyish; Genta mistakes her for a man, and Sonoko comments she has a petite figure. Later, Genta, Mitsuhiko and Hattori comment that her bosoms are rather small. Sera also has an uneven tooth that shows when she smiles.

Sera first met Sonoko, Ran, and Conan on a bus after she was mistaken for a groper. After Sonoko declared Sera was the groper, Sera and Ran got into a fight, with Sera's Jeet Kune Do holding even against Ran's karate. Conan and Sera cleared up the misunderstanding by pointing out the real groper. Sonoko then mistook Sera for a boy, an impression which wasn't helped by Sera declaring that Ran was "his type". Sera and Ran both discovered they were heading to the same hotel, about which Conan is less than pleased.
Sera finds out the hotel she is staying at doesn't have a room available and complains at the front desk. A man then falls into the parking lot and dies. Conan runs to the source of screaming while Sera told the guard to watch the elevators before running to the roof. She immediately declares the crime to be a murder, giving her reasoning. She then reveals her name, Sera, that she is a detective, and knows Conan is a detective as well.

Inspector Megure is not pleased to have another high school detective underfoot but lets Sera and Conan investigate regardless. After listening to the suspect testimony, police observations, and examining the crime scene, Sera announces that she has solved the case.

However, Sera's deduction leaves out a critical detail; Conan is therefore forced to use Shinichi's phone to call his own, give Inspector Megure Conan's phone, and speak through Shinichi's as Shinichi using the voice-changer bow tie. Shinichi figures out the detail that had Sera stumped, although a look she gives Conan as he runs off suggests her omission was possibly intentional, and once during the phone conversation she tries to trick Shinichi into admitting that he is physically present at the crime scene instead of being explained the details by Conan and Megure.

The following day, Sera transfers to Teitan High School, surprising both Ran and Sonoko. She was rather popular at school surrounded by students asking her questions about herself.

According to Sonoko, Sera has become very popular at Teitan high for being "cheery, sociable, boyish, and cute...and on top of that, she is a jeet kun do-using female detective!" One classmate compares her to Shinichi Kudo who has been taking a break from school. Sera tells inquiring classmates that she has been staying in America with her parents since three years ago, but "rebelled" because she would rather live in her Japan where she was born and raised. She sneaks up behind Sonoko and Ran after school because she wanted to speak to Conan at the Mouri Detective Agency. At the agency, Sera is unhappy to hear that Conan and the rest of Detective Boys are staying at Agasa's house and will be camping the following day. She settles for asking Kogoro if Conan is always at his side when he solves cases, hinting that she suspects Conan is the real brains behind "Sleeping Kogoro".
Just as Sera is about to walk out the door, three female mystery writers and a man enter the agency. After a moment of confusion, the man suddenly fires a gun into the roof and takes the detective agency hostage. His demands are that Kogoro figure out which of the three writers killed his sister at a ryokan one month ago. The quick thinking Sera sidles up to Ran and tells her to go for the man's gun after she takes his legs out. Sera's leg sweep sends the man to the floor, and Ran removes the gun from the man's hand with a kick; however, Sera leaps back when the man reveals he has bombs strapped around his chest and will detonate them if they try to stop him.

Meanwhile at Agasa's, Haibara is angry that Conan used Shinichi's voice to solve a case around the suspicious Sera. Conan's response is that Sera is familiar somehow, like they have met before or she looks like someone, and Conan feels she isn't an enemy. Genta and Mitsuhiko told Conan they saw a high school student walking home with Ran, so the jealous Conan calls Ran's cellphone to hear about it from her.

The hostage taker man orders Ran to answer her phone, but Sera snatches the phone away and says hello to Conan (who is shocked that Sera is with Ran). Sera then tricks the hostage taker and keeps the line connected so Conan can listen in by closing Ran's Sea Cucumber Man cellphone strap in between the screen and keypad of the the flip phone.

Sera asks a few insightful questions about the case; however the hostage taker man discovers Ran's phone is still connected. Under gunpoint, Sera steps in front of Ran and takes the blame, but Conan, using Shinichi's voice, says he ordered Ran to do it. Sera is mystified by why Shinichi is now on Conan's phone. Sera meanwhile spots a glint of light across from the detective agency and declares that the case will come to an end without Shinichi's help.

Sera explains to Ran that she secretly kept the call to Conan connected so he could call the police and research into the case. While Sera is still surprised that Shinichi was on the other end of the line instead of Conan, she had initially hoped that Shinichi would somehow be able to talk down the would-be-murderer. She suspects that Shinichi has already figured which one of the suspects is the murderer in the ryokan case, but Shinichi is unable to reveal the truth because the hostage taker would then kill the named culprit and then himself. Sera's plan changed when she noticed the lights from the police snipers on the building across from Mouri Detective Agency. She explains to Ran in detail the names and functions of the various police divisions responsible for hostage situations, and tells Ran in a roundabout fashion that this situation will end with the hostage taker being killed by the police.

Sera launches a plan to bring the hostage taker into the snipers' range by telling him he should charge Ran's phone battery. Ran foils Sera's intentions by shutting the curtains, blocking the snipers' shot. To Sera's utter astonishment, Ran tells her that she doesn't want to see anyone die in front of her and declares that "Shinichi won't allow anyone to die. He absolutely wouldn't!"

Sera and Ran take the opportunity to disable the hostage taker when he loses his composure and grip on the detonator after Shinichi tricks him into believing his sister committed suicide. Sera yells for the waiting bomb squad to secure the area. With the hostage taker arrested, Shinichi then reveals the true culprit. Sera realizes the mistake in her deduction and explains the correct timeline of events before the murder. Sometime soon after the conclusion of the case, Sera, walking with Ran and Sonoko speculates aloud that there must be some reason Shinichi left Agasa's before Ran could meet him there. She then exclaims that "due to what just happened, she really gets it", that Conan and Shinichi are on very good terms with one another, and that Ran "is tougher than Sera thought". Conan isn't sure what to make of these last comments.

Sera stops Genta and Mitsuhiko outside of Agasa's house to ask them if they are acquaintances of Professor Agasa. The topic of Shinichi comes up when she talks to Mitsuhiko and Genta about the prior hostage case. Mitsuhiko mentions that Haibara told them to keep Shinichi's involvement secret. After asking about Haibara, Sera mentions that she saw Haibara in one of the professor's online videos. Next, Sera asks who is currently living in the Kudo house because she saw the curtains shift slightly. The Detective Boys tell her that Subaru Okiya has been staying there since his apartment burnt down.

Sera cryptically comments with a smirk on her face, "And here I thought that someone had just settled in without permission...But it seems I was just getting worked up over nothing..." while looking up at where Subaru Okiya is hiding.

At the end of the case, Sera is in her hotel room deleting various files. One of her deleted files was a still image from Agasa's video blown up to show Haibara reflected in Agasa's glasses. This indicates that she is not only keeping an eye on Conan but also on Haibara. "Delete... Delete... For data, at least is an easy task to accomplish...", were her words while she was doing it.

The case opens with Ran talking to Sera about Heiji Hattori who is stopping by for a visit. Sera is curious whether Heiji or Shinichi is the better detective. After Heiji is introduced to Sera, Kazuha then calls Heiji and tells her that she is stuck at a restaurant because someone died and a foreigner Andre Camel is keeping everyone from leaving. Sera proposes Heiji and Shinichi (via Conan's cellphone) have a deduction match. At the crime scene, Sera becomes curious about the foreigner, Andre Camel who secured the area. The police and Conan reveal Camel is an FBI agent and Sera takes interest. Meanwhile, Camel finds that Sera looks familiar, but can't quite place why. He takes a picture of her and mails it to Jodie and James Black who are waiting outside. Jodie and James Black think Sera resembles someone too, but only James Black correctly identified Sera as female.

Meanwhile Sera is busy helping with the case, asking questions and making comments about various deductions. Heiji nearly slips up with Conan's identity in front of her earning a pointed question from Sera, but Heiji rescues himself by saying he thinks of Conan as Kudo when Conan gets smug have hearing Shinichi's deductions over the phone. Sera doesn't seemed to be fooled though, her thoughts show that she seems to know Conan, not Shinichi, is the one solving the case while watching Conan come to his final conclusion.

Conan, Heiji, Sera, and the rest of the group return to the Mouri Detective Agency after the poisoning case at Danny's restaurant. Heiji reveals the case that brought him to Tokyo; he received a mysterious letter signed in the name of a person who was murdered in Karuizawa requesting an investigation. Sera takes an immediate interest in the case and wants to tag along, but Heiji refuses saying that the people he is visiting are only expected five people. Sera is peeved at being left behind.

Sera is walking with Conan, Ran and Sonoko. While they wonder why Kogoro has been coming home late, Sonoko thinks he's found himself a mistress. Sera thinks that he is just investigating a case. When an old lady named Takae Kiritani comes, she claims that Kogoro has been helping her. Sera asks what he does for her to which she replies that its small things like helping around the house. Sera isn't seen again for the rest of the case.

During a murder case at Mouri Detective Agency, after meeting Kogoro's new apprentice Tooru Amuro, Megure comments that the number of detectives around Kogoro has increased again, referring to Sera. Amuro takes interest in Sera. Later, Kogoro and friends go over to a suspect's apartment. Sera calls Ran after hearing about the murder on the news because she is worried about her and Conan. The call has an usual amount of static which alerts Amuro that there are listening devices present. Amuro abruptly hangs up Ran's phone on Sera. Meanwhile, Conan intentionally gets himself kidnapped by the primary suspect. After Ran enables calling again, Sera calls back immediately and is very upset because she was worried something had happened to Ran. Ran tells her that Conan has been kidnapped, and details to Sera the murder at Kogoro's agency. In order to figure out where the kidnapper is headed, Kogoro and Amuro search the apartment and decide to go to the address of one of the other suspects.

Sera arrives at suspect's home on her motorcycle, but just misses Kogoro and the gang leaving. She hears the elevator descending and rushes back downstairs in time to follow Amuro's car. Meanwhile, the culprit has been driving around with Conan while Haibara has been directing Okiya's car towards them using the criminal tracking glasses. Okiya catches up to the kidnapper and relays what the car looks like to Kogoro. Amuro sees the suspect's car heading in the opposite direction so he quickly wheels around after it. Sera, who has been following Amuro's car this whole time, u-turns after Amuro and continues chasing. Amuro gets in front of the suspect's car and stops it. The suspect gets out of the car holding Conan at gunpoint, but Sera drives up onto the roof of the car. She swings her motorcycle around so that the rear wheel slams into the woman's face knocking her unconscious. With tears of relief, Sera hugs Conan, happy he is safe. Amuro, Okiya, and Vermouth look on.

Sera is walking with Sonoko and Ran, and Ran is talking by phone with Conan. Sera hears Haibara's voice in the background and becomes curious. She asks the two others what Haibara is like, and Sonoko says Haibara is like a woman in a child's body.

When Ran hangs up her cellphone, the topic switches over to Amuro. Sera says to Ran she wants to meet Amuro because she never got a really good look at him from the last case, but Sonoko thinks she wants to meet Conan. instead. Ran says Shinichi and Conan are big fans of Sherlock Holmes. Sera thinks about that she has known that for a long time.

Suddenly, Sera sees Scar Akai in the crowd ahead. She runs after him, but she can't catch him. Ran wonders who Sera was chasing, but Sera replies she thought it was someone she knew, and silently appends in her mind that it would be impossible for the man she was chasing to be the person she thinks it was.

Sera meets Subaru Okiya at Shinichi's house and she finds him suspicious. She began to think there is a woman at Kudo's house because there are a hair elastic, lipstick in a glass and a long hair in the sink trap. After that, all of them solved a case together that is similar to a case that Shinichi Kudo's father dropped out 10 years ago. It was revealed to be a theft case. Both Subaru and Sera had got more suspicious of Conan and the identity of Shinichi Kudo. At the end, when the criminals were knocked, she saw Ran and Conan and she thought she was a 'bad kid', after all.

She went camping when she meets Professor Agasa and Conan. The Detective Boys were lost. Sera and Conan found the two policemen finding the corpse. After she and Conan solved the case, she and Conan rushed towards the burning cabin. Conan and the Detective Boys were talking about how they got safe. Mitsuhiko pointed the way were their savior went. Sera then began to ask what kind of woman is their savior. She seemed to be surprised when she saw her on Mitsuhiko's cell phone.

Sera finally meets Haibara, and Haibara has a bad feeling about her (although it could have been due to Scar Akai spying on them from behind the door just then). Later when a murder occurs on the Bell Tree Express, she and Conan investigate. Sera takes a video recording of the suspects running so she can show it to the detective boys in order to ask them which one had the closest gait to the masked suspect from earlier, but she is intercepted first by Scar Akai in the hallway. She stops and angrily asks him who he is. Scar Akai simply replies that she hasn't changed, reveals his face to her, and refers to her by her first name, "Masumi". In her shock Sera calls him "Shuu-nii", signifying that Akai is Sera's older brother. She questions Scar Akai about what happened, saying that she heard he had died. Scar Akai then tasers her unconscious, stating that he was hoping for that response. Scar Akai later is revealed to be Vermouth in disguise, explaining why he attacked Sera.

Sera accompanies Conan, Ran, and Sonoko to the location of Kaitou Kid's next heist: a museum where the Blush Mermaid, a gem adhered to the shell of a turtle as a last ditch effort by a an Italian actress in an accident at sea to save her turtle by encouraging someone to rescue it. Before checking out the museum, Sera asks Ran if she saw a strange man in black when she found the hat on the Belltree Express. After the group arrives at the room where the turtle is being held in a large aquarium, Inspector Nakamori pulls Sera's face to see if it is a mask worn by Kid. Annoyed by Nakamori's mistaken gender assumption and having her face pinched, Sera knees him in the privates ostensibly to prove he isn't Kid. Sera then runs off to the bathroom. Later, when Kid makes his move, Sera is one of many caught in his trap: the rug on the floor is pulled up by strings so that it pins everyone standing on it to the front of aquarium. As soon as the rug drops, everyone sees the tank is empty except for a card left by Kid. This leaves Conan and Sera quite dumbfounded as to how Kaitou Kid could have removed the turtle. Later, Conan reveals that Sera is really Kaitou Kid, and he had made a critical error in his acting by assuming Sera was a male. Kaitou Kid had locked the real Sera in the men's bathroom after knocking her out with a stun gun. Upon gaining consciousness, Sera escapes her bonds, rushes out of the bathroom, and gives a still disguised Kid a fierce kick to the face. After Kid escapes, Sera is relieved she recovered her hat, which she thinks is special because it somehow has the same feel as her brother Shuichi Akai's hat.

Conan, Ran, Sonoko, Kogoro and Sera go to a live cooking show. Conan wants to ask something important to Sera, but a murder gets in his way. While solving the case, Ran realises that Sera and her might have met each other before, since Ran thinks of waves in the beach each time Sera gets away. At the end of the case, Conan asks Sera if they had met each other before. Sera smiles and says she doesn´t know, but actually she thinks "Of course we have, but I can´t tell you until the time comes..."

After being hired by a classmate, Kitao Keiko, Sera is investigating to see if the boyfriend of Keiko's sister has fully committed to their relationship. However, as the atmosphere is rapidly changed by the murder, Sera and Conan start to investigate the crime scene. When Conan has finally deduced who the culprit is, he also observes Sera making a call with someone saying "...Say, my deduction... It's not wrong, is it?".haha

At a Bowling Center with Conan, Ran, Sonoko and Kogoro, Sera is introduced to Sonoko's boyfriend Makoto. Shortly before, Sera mistook Makoto for a stranger being "overly friendly" with Sonoko, therefore defending her with Jeet Kune Do. Explaining Sera has been taught Jeet Kune Do by her older brother, she also reveals that besides her assumingly dead brother she has a second-oldest brother. Furthermore Sera explains to Conan that her brother also advises her on cases by phone. After successfully investigating the crime scene with Conan, Sera steps aside with her smartphone and types in the message "It seems like he's also arrived at the truth... But whether or not our deductions are the same - lately I've been losing confidence in that regard...". When the recipient writes back "Who is he? I'd like an explanation!", Sera takes a picture with her smartphone. However, the recipient's answer "If it's him, there's no problem." reveals that he is familiar with Conan. It is heavily implied that it is the same person Conan saw Sera making a call with in File 857.

Sera was revealed to be Shuichi Akai's sister on the Bell Tree Express after a confrontation with Scar Akai and while sleeptalking.

*Sera has bags under her eyes identical to Shuichi Akai's.

Masumi Sera's name is also incredibly similar to Mobile Suit Gundam character Sayla Mass (セイラ・マス, Seira Masu). Akai's name is derived from Sayla Mass's older brother's name, Char Aznable.

Conan said he has a feeling he had met her before. "Somehow I feel like we've met somewhere before, it might be that person resembles someone I know, that's why the feeling that we've met before is on my mind..."

Andre Camel and most likely James Black seem to recognize her from somewhere. On another interesting note, James Black was the first to recognize that Sera was a girl. Everyone else thought that she was a guy when they first saw her. Since James was Akai's boss, he would most likely know that Akai has a younger sister and what she would look like.

Sera lived in Japan until three years ago when her family moved to America. This matches with the time when Akai was infiltrating the Black Organization. The family's move to America could be the FBI's attempt to protect them should something go wrong with Akai's mission.

In Chapter 801, Sera chased after Scar Akai who appeared while she was walking with Ran in front of the Mouri Detective Agency. Although, Scar Akai hid before she could find him, she told Ran that she had just seen "someone she knew".

In Chapter 859, Sera, when being asked who taught her Jeet Kune Do, answers that her older brother did. Consequently, Conan asks Sera: "But, didn't you say your older brother was dead?" This leads to Sera remarking "Yeah... That's what I heard." also further supporting the theory that Sera is in Japan to investigate her brother's death.

In Chapter 801, Sera chased after Scar Akai who appeared while she was walking with Ran in front of the Mouri Detective Agency. Although, Scar Akai hid before she could find him, she told Ran that she had just seen "someone she knew". She then thinks there is "no way it was possible" regarding the man she saw, which would make sense if she thought Akai was dead. This implied she wasn't Bourbon, since Bourbon believes he is the only one who can kill Akai, implying that Gin might have failed to do so. Hence Bourbon wouldn't think that it was impossible to meet Akai again in the street.

Sera is interested in Conan's abilities as a detective and has been gathering information on him and his friends. She may be suspicious that Conan is Shinichi Kudo. Despite her initial suspicious presentation, Conan felt like she wasn't a bad person and so didn't mistrust her. Conan at one point questions her if they've met before, but she denies this and secretly thinks, "Now's not the time". In fact, Sera is quite fond of Conan, and treats him like her younger brother.

Sera met Shinichi and Ran when she was younger and knows Conan is ShinichiEdit

Sera knew Conan and Ran's identities before they introduced themselves. Although she claimed to know Ran from Karate tournaments, she recognized Conan as a detective and anticipated his skill. Sera admits that she has met Conan before, but she can´t tell him until "the time" comes. Since Conan didn't exist until Shinichi shrunk, Sera must have met Shinichi some time in the past, and she recognizes him as Conan. Conan realizes he met Sera before because he finds her snaggletoothed smile familiar, but she refuses to tell him where they met prior. Ran appears to have met Sera as well because Sera's figure as she runs away reminds her of "sounds of rippling waves, as if some sort of magic were at work."

In Chapter 771, it is revealed that she also knows Professor Agasa, although she calls him "Professor what's his name".

Sera initially had an interest in Haibara. This is strange because Haibara didn't exist prior to Shiho shrinking. The knowledge of Shiho should have been secret to her as well, because Shuichi Akai's infiltration of the Black Organization was a secret. If Sera doesn't even know the details of her brother's death, why should she know about Shiho? Sera may recognize Haibara from pictures of Conan and Haibara that Akai took back during the Vermouth arc. It is standard procedure in the US to send the personal belongings of the dead back to their families. If Akai mixed these pictures in with his own things when he took them out of his truck before meeting with Kir, it's possible they were overlooked when the FBI sent Akai's things to his family. If Sera was interested in finding out how and why Akai died, she would begin by researching the people in those pictures and those connected with them in hopes of finding clues.

Masumi Sera's (世良・真純 ,Sera Masumi) name comes from the Mobile Suit Gundam character Sayla Mass (セイラ・マス ,Seira Masu).The kanji for Sera's last name mean 'good world'. The kanji for her first name, Masumi, mean 'true' and either 'pure' or 'net.'